In the drilling of deep wells in earth formations, many different type of earth formations are encountered and boring or drilling operations in each of these types of formations require differing boring equipment. For example, in loose or unconsolidated earth formations such as gravel strata, it is desirable to utilize integral drill bits having a plurality of blades for cutting away the formation. Where consolidated, very hard earth strata is encountered, for example, in deep earth formations, it is typically desirable to employ drill bits having a plurality of rotary cone cutters having multiple projection cutter teeth. The teeth of the rotary cutters are cooperatively associated so that the earth formation is cut away as the drill bit is rotated at the extremity of a string of drill pipe extending from the drilling rig to the formation being drilled. The typical rotary cutter type drill bit or "rock bit" includes a body portion from which depend three legs. Spindles or cutter supports extend inwardly toward the center line of the drill bit from each of these legs. Rotary cone type cutter elements having cutter teeth formed thereon are typically rotatably secured to each of the supports or spindles and are oriented in such manner that the cutter teeth thereon engage and cut away the earth formation as the bit structure is rotated by the drill pipe.
One of the paramount disadvantages of drill bits having rotary cutters is the inability of the cutter bearings to withstand the severe wear inducing conditions to which the drill bit is typically subjected. As drilling operations occur, rock bits are subjected to severe impacting and vibration as well as other wear inducing factors that are highly detrimental to the service life of the rotary cutter bearings and other components of such drill bits. At times, much of the weight of the drill pipe to which the rotary drill is connected may be caused to act upon the cutter, subjecting the cutters and their bearings to tremendous mechanical loads. It is therefore desirable that rotary drill devices be provided which incorporate bushings having the capability of withstanding extremely high forces, excessive vibration as well as remaining serviceable during high temperature operation. Further, the extremely abrasive environment in which such drill bits operate cause the lubricant seals to wear at an accelerated rate. When this occurs, abrasive particles invade the seal interface, quickly inducing seal breakage due to seal wear. The bearings or bushings of the roller cones will then fail at an accelerated rate.
Typically, the drill bodies of rotary cutter devices take the form of integral cast or forged structures that are very expensive to manufacture because of the complex configuration thereof. It is also desirable to provide a rotary drill bit construction having a body structure of exceptional strength and durability and yet being of relatively low cost. Drill bit cost is also adversely affected by the typical requirement for expensive materials for most of the structural components of such bits. For example, an expensive bearing quality material may be required for the drill cutters of the entire body structure of the bit if any part thereof is to define a wear resistant bearing surface.
It is therefore a primary feature of the present invention to provide a novel rotary cone cutter type drill bit construction that allows optimum utilization of materials for the various components thereof to ensure optimum drilling capability and exceptional service life.
It is also a feature of the present invention to provide a novel rotary cone cutter type earth boring drill construction wherein a unique cutter supporting bushing and spindle assembly may be connected to structural components of the drill body by welding or may be formed integrally therewith, if deserved.
Among the several features of the present invention is contemplated the provision of a novel rotary earth boring drill construction incorporating bushing and spindle assemblies that, through optimum use of material, are capable of withstanding extremely severe operational loads.
It is an even further feature of the present invention to provide a novel rotary earth boring bit construction and novel method for assembly thereof which promote the low cost and exceptional reliability aspects of the drill construction.
It is also an important feature of the present invention to provide a novel rotary earth boring bit construction whereby rotary cutter elements are assembled to respective spindle and bearing assemblies utilizing controlled changes in dimension by heating various drill bit components and/or cooling interrelated bit parts to achieve optimum fit at normal temperature.
It is also a feature of the present invention to provide a novel rotary earth boring drill construction whereby mechanical locking means may be provided to ensure positive locking of rotary cutter elements to the spindle bearing and thereby ensure against separation of the cutter elements by vibration and other operationally induced forces.
It is a feature of the present invention to provide a method of manufacturing a rotary cutter type drill bit wherein cutter, and bushing/journal assemblies may be developed prior to attachment thereof to the drill body.
Other and further objects, advantages and features of the invention will become obvious to one skilled in the art upon an understanding of the illustrative embodiments about to be described and various advantages, not referred to herein, will occur to one skilled in the art upon employment of the invention to practice.